Historical ecologists working in the Neotropics argue that the present natural environment is an historical product of human intentionality and ingenuity, a creation that is imposed, built, managed and maintained by the collective multigenerational knowledge and experience of Native Americans. In the past 12,000 years, indigenous peoples transformed the environment, creating what we now recognize as the rich ecological mosaic of the Neotropics. The prehispanic savanna peoples of the Bolivian Amazon built an anthropogenic landscape through the construction of raised fields, large settlement mounds, and earthen causeways. I have studied a complex artificial network of hydraulic earthworks covering 525 km2 in the Baures region of Bolivia. Here I identify a particular form of earthwork, the zigzag structure, as a fish weir, on the basis of form, orientation, location, association with other hydraulic works and ethnographic analogy. The native peoples used this technology to harvest sufficient animal protein to sustain large and dense populations in a savanna environment.